The Extinct Ice Age Mammals of North America

JERRY BALDASTY: Good evening. Hi. I’m Jerry Baldasty. I’m the interim provost and
executive vice president. Welcome to the 40th annual
university faculty lecture. Every year, the University
of Washington faculty members select one of their peers to
present this distinguished lecture. Over the past four
decades, we’ve seen an impressive
list of presenters give this prestigious lecture–
historians, doctors, artists, engineers, and many others. This is the highest
honor the faculty can give to a member
of their own ranks, and so this is a very special
evening for all of us. This year’s recipient,
Donald Grayson has been an
anthropology professor at the University of
Washington since 1975, teaching archeology both in
the classroom and in the field. He’s a true leader
in this profession and has been so for decades. He’s researched and
written extensively on a variety of sites,
time periods, and subjects, but he’s most recognized for his
research in southwestern France and the Great Basin of
western North America. In addition to
this academic work, there are many
students who can speak to the impact of his
teaching and mentorship. Some of these would be
the undergraduates who enjoyed his classes on the
prehistory of the arid west and prehistoric extinction, or
they might be among the 22 PhD students he has mentored
throughout his career, and he has helped them
find fulfilling employment across the country. He’s an incisive and
thoughtful leader. He cares deeply about
discipline and the people whose lives it touches. Aside from all of
this, he is also an engaging, thoughtful
speaker who inspires curiosity in students and peers alike. We are so lucky
to have you here. Please join me in welcoming
our university faculty lecture professor,
Donald Grayson. [APPLAUSE] DONALD GRAYSON: I will try
to live up to part of that. [LAUGHTER] The picture on the
bottom of the screen is a picture of a mammoth being
excavated in the Black Rock Desert of northwestern
Nevada, the same Black Rock Desert where the Burning
Man Festival is held. Almost everybody who
grows up in this country learns about this
particular animal, the mammoth, alongside
animals that lived with it. Saber toothed cat is
an obvious example. A mastodon is
another possibility. More recently, if anybody
has seen the movie Ice Age, you’ve seen what
I actually think is someone knows something
about these animals– are really good, perhaps,
caricatures of these animals– Manny the mammoth, Diego,
the saber toothed cat, Sid, the giant ground sloth. Everybody’s heard
of these animals to one degree or
another if you’ve grown up in North America. That may be all you know. You may not know when
they became extinct. You may not know why
they became extinct, and I will say
now, although we’re going to come to
this later, if you have heard that
they became extinct because they were hunted
to death by human hunters, I would claim that
you still don’t know why they became
extinct, but I will return to that later. These extinctions have
been the focus of research for over 200 years. In fact, some of these animals,
including the mammoth and one of the North American
ground sloths, was critical around
the year 1800 in establishing the fact that
extinction could actually occur in the first place. By the 1870s, the great
evolutionary biologist Alfred Wallace was able to point this
out, what’s up on the screen– that some time in the
recent past the earth had lost some of its hugest,
fiercest, and strangest animals. He marveled at this. If he were still alive, today
he’d marvel at it even more. He’d marvel at an
even more because we know so much more
about these animals than we did when he was alive,
but he’d also marvel about it because we still don’t
understand any more than he did why these extinctions occurred. I’m going to focus on North
American extinctions here. North America lost
37 genera of mammals as the ice age came to an end. When Wallace said that these
were recent disappearances, in modern terms, he could have
said that these were late ice age disappearances. The ice age is
the period of time that lasted from 2.6
million to 10,000 years ago. It was characterized by
the alternating advances and retreats of massive
glaciers on many parts of the earth’s surface. The extinctions that
I’m going to talk about were extinctions that
occurred– oh, I’ll be general about it now–
between roughly 30,000 and 10,000 years ago. There’s only one term that I
have to define besides ice age, and that’s the term
genera that I just used. Everybody has run across
this term, the term genus. The plural is genera. Similar species are lumped
into, grouped into a genus in biological classification. Genera are grouped into families
and so on up the hierarchy. Once having defined
that, I can go back to what I just said– that
toward the end of the ice age North America lost
37 genera of mammals. It’d be fun to just talk
about North America. It is fun to just talk
about North America, but I also want to point
out that it wasn’t only North America where
this was happening. It was happening in Eurasia,
but more important for us it was also happening
in South America, where 54 genera of mammals were lost. Because some of the
North American mammals were also found in the south
and some of the South American mammals were also
found in the north, if you count up the total
number of genera of mammals that were lost, you get 77. That is a huge– that is a huge
part of biological diversity to have been lost at
the end of the ice age, and as I said
before, we’re still trying to figure out why
and how that happened. In addition to
that– and this is going to become really
obvious as we go along– one thing that characterized
these losses is the fact that the animals were all big. Well, all is a bit
of an overstatement. Three fourths of the
animals that were lost weighed 100 pounds or more. We’ll see that some small ones
also went out of business, but we’re also going to see
that the overwhelming majority of these animals were
really, really big. My goal today is to
spend an hour– I’m going to look at my
watch and see when that’s going to be up– trying to
clarify some of these issues, and I know that I’ve
got more to talk about. I could talk about
this stuff forever. I teach a whole
course on this stuff. I know I’ve got more stuff
to talk about tonight than we have time to talk about,
and when the hour is up, I’ll just stop. [LAUGHTER] As I said, 37 genera of mammals
were lost from North America. Six of these– and
we’ll see what they are. Horses are one of them–
live on elsewhere, but when they became
extinct in North America, they never appeared
here again unless they were reintroduced later on. I’m going to give you a
rundown of all these guys, and I’m going to start
with the cingulates. Think armadillo. Cingulates are animals
with external bony armor. These are South American
animals, some of which, just like armadillos,
made it north. There are two animals
very closely related to armadillos
called pampatheres. If you saw one, you’d
immediately think armadillo, but you’d also
think something else that I can’t repeat here because
of the size of these animals. This is an armadillo that was
six feet tall, three feet long, and weighed between
500 and 600 pounds. I am not, by the way,
making any of this up. Northern pampatheres
were southern animals. They made it to
southern North America. The southern pampathere
about the same size. There is its shell, but this
is a South American shell. Southern pampatheres are not as
well known for North America, but they did make it here. Then there’s this next guy. Glyptodont– glyptodonts
are also South American. These are armadillo-like
in the sense that they also have
external body armor, but unlike the armadillos,
this external body armor is not flexible. These guys had carapaces
like tortoises. They also were almost
literally the size of Volkswagen Bugs, the cars. Weighed 2,400 pounds–
that carapace was fused to their inner skeleton. They hung around water. These were absolutely
remarkable animals. I don’t know if you can see
that picture on the lower left. If I start free
associating like this, we’ll never get
through anything, but if you can see this
picture on the lower left, I stuck it in here
because I love it. This is a picture
of a glyptodont that was a reconstruction
of a glyptodont that was made in the
1930s for work being done by famous paleontologist
George Gaylord Simpson. In the 1930s, it was already
known that some South American glyptodonts had tails that ended
with mace-like projections, but in the 1930s,
they had yet to find the end of the tail of the
North American glyptodont. So they hid it behind
a bush because they didn’t know what it looked. [LAUGHTER] Once it was found,
it was discovered that its tail ends without
the mace-like projections. It’s simply rounded. This is its distribution. Sid the sloth– the
movie Ice Age amazes me. I’ve actually looked on the
web to see if I could find out who knew enough
about the ice age to do those reconstructions
because they’re really good. There’s a glyptodont in there. There are South American
animals in there that North Americans
generally have never heard of. It’s a great movie. Sid, the ground sloth, is
meant to reflect the fact that North America
during the late ice age had four genera of
huge ground sloths. When we think of sloths, we
think of slow moving, tree hugging animals that, if they’re
fat, may weigh 20 pounds. That is not the case for the
North American ground sloth, and the North
American ground sloths as a whole are smaller than
the ones that went extinct in South America. I’ll start with a megalonyx,
Jefferson’s ground sloth. Here’s a reconstruction done by
a very talented paleoecolgoist friend of mine, Wally Wolfenden. We’ll be seeing a bunch of
his reconstructions today. This is a reconstruction
of megalonyx. Its name means great claw. It was given that name by
Thomas Jefferson in 1797, and you can probably see
why he called it that. He called it that because
of these great claws. He didn’t recognize
it as a sloth. Not surprising. This is 1797. He thought it was a carnivore. He was wrong about that. He also didn’t realize
that it was extinct. He argued that if it had once
existed it must still exist, and as I said before, some
of these animals, including megalonyx were used to argue
that extinction was real. When Jefferson was
writing, he did not yet believe that that
could be the case. Megalonyx– widespread in North
America, as you can see here, coast to coast. This one– in my extinctions
class that I teach, I have an election every year. Not as fancy as the
one I had this year. This year’s was really fancy. We had a primary election, and
then we have the final election to see which of these 37
genera– one, the students– I voted, too– all
of us– would most want to see if they
could see one alive. I voted for glyptodonts. My students got it wrong, and
they voted for eremotherium. [LAUGHTER] Eremotherium had the
height of a giraffe and the bulk of an elephant. It is eastern in distribution,
mostly southeastern, but there’s one curious
record from coastal New Jersey that you can see on this map. If I had to have
a favorite sloth, it would be this
one, nothrotheriops. It is shown here eating the
fruits of the Joshua Tree. It’s shown that way because we
know that it ate those fruits, and we know that it ate
those fruits for something I’ll talk about in a minute. This was the smallest
of the ground sloths, the smallest of the North
American ground sloths. It was also western
distribution. By the way, I’ll point out that
that odd shaped blob that you see on the west side of the map
is a region called the Great Basin. If we have time tonight, if I
don’t free associate too much and run over time, I’ll
talk about the Great Basin towards the very end. That’s the distribution
of nothrotheriops, the smallest North
American ground sloth. We know what it
ate because we have its turds, if I can say that. Here is one of them. Nothrotheriops, the
Shasta ground sloth, had the friendly
habit of pooping in caves in the dry
west, in the arid west, including caves in
the Grand Canyon. This particular one
comes from Rampart Cave in the Grand Canyon. You can pull these things apart. You can identify– you
can radiocarbon date them, and you can identify the
plants that are in them. As a result, we know a lot
about ground sloth diets. And just to free associate,
there must be men in here– and I’m saying men because
this is more common in men than in women– men in
here who get kidney stones. Most kidney stones are
oxalate kidney stones. I get them, so I’m
familiar with them. Most of them are
oxalate kidney stones. Yuccas and agaves are
loaded with oxalates. When these pieces of dung were
first analyzed in the 1930s, a botanist and a chemist
combined to do it, and they discovered
that these things were– they did the chemical
analysis and discovered that these things were
also full of oxalates, and those oxalates are
coming out of the plants that they were eating. How ground sloths didn’t get
kidney stones is beyond me. I’d love to know. This is paramylodon. This is the fourth
of our ground sloths. This is the most abundant
ground sloth at Rancho La Brea. It’s part of a family
called the mylodon ground sloths, all of which are
characterized by the fact that their skins have little
bony pebbles embedded in them. In fact, that skin that
you see on the lower right was found in the late
1800s in southern Chile, and it led to the possibility of
that ground sloths might still exist and to an expedition to
find them still on the hoof. They didn’t, but every so often
that possibility reemerges. Perhaps the argument is they
still exist in the deep Amazon. In North America,
they were clearly gone by 10,000 years ago. That’s the distribution
of paramylodon. We even have paramylodon
footprints from– and I’m not making this up. This is going to sound
funny, but it’s true. This dot right here is
the Nevada State prison, and there were
footprints found there in the late 1800s that
were thought at first to be human footprints, and
within a decade or so were recognized to be mylodon
ground sloth footprints. They’re the only footprints
of a sloth, as far as I know, that are known
from North America. The carnivores– smilodon,
the saber toothed cat, is one of the iconic
mammals of North America, along with the mammoth,
but there were seven genera of carnivores that were lost. The short faced
skunk– paleontologists are really good at giving
common names to animals. The short faced skunk is
called that because it’s a skunk with a short face. It’s not very well known. There are only seven sites of
it known from North America. Cuon, the dhole, is
a hyper carnivore that is doing OK– not great,
but OK– in southern Asia today. During the ice age, it
found from northern Spain all the way across into
Northeastern North America– pardon me, northwestern
North America. And then if you
look closely, you’ll see that one site in
Mexico way down here– every so often somebody
gets it in their mind that that can’t possibly
cuon, and they go look at it, and sure enough it is. It has to– these
were not birds. It has to have lived
someplace in between. All the work I did
in the Great Basin– the site’s been known
for a long time. I always had my
eyes open for cuon. It’s an animal that I would run
across in the paleolithic sites that we worked on in France. Nobody’s found one in between. It had to have been there. Somebody will find
it sooner or later. Tremarctos, the
Florida cave bear. Tremarctos still exists. It’s called the Andean bear. It still exists in the mountains
of western South America. I believe there’s one
in the Seattle zoo. It’s also called
the spectacle bear. This is a South American bear
with its closest relatives, and it’s distribution
during the late ice age was South American. It was closely
related to this guy. Whoops, wrong button. This guy, the giant bear. The giant bear is called
that for a good reason. The giant bear was the longest
land carnivore of the late ice age anywhere in the world. I put 1,500 pounds on
there for its weight, but there are some whose
weight has been estimated as high as 2,000 pounds. People argued for a long time
about what its diet might be. Argued is the wrong
term– pondered, did research on what its diet
might be, and in the end, we’ve learned so much about it
that the conclusion is obvious. This bear ate whatever
the hell it wanted to. [LAUGHTER] Widespread– coast to coast,
and up into the northwest. Although one thing that we
know is that these records in the far northwest date to
the 20,000s while ones down here date to as late as
about 11,000 years ago. They seem to have become
extinct up here before they became extinct down there. The saber toothed cat–
one of animals– Diego in the movie Ice Age. Massive, massive animals
weighing 500 pounds. Larger than an African
lion with those long sabers protruding from its mouth. The sabers had
serrations on both sides like pinking shears
on both sides. Narrow, powerful cutting tools. These animals also had
really powerful front limbs built in such a way as to
be able to resist twisting motions from while they
were killing their prey with their front limbs. These animals were probably
ambush hunters, lurking for their prey to walk by. There are also 2,000 of them
roughly at Rancho La Brea. That fact suggests that
they were probably social, as well– a probably
social pack hunting animal. There is their distribution. I should say with all these this
is their known distribution. Surprises can
always be in store. Homotherium was
called a scimitar cat. It also had those
protruding teeth, but they were smaller than the
protruding teeth of the saber tooth. Homotherium was really
widespread in the ice age Africa all the away across
down into South America. Homotherium was a long
legged powerful cat, short tailed– long legged,
powerful, short tailed cat. Pretty clearly
ran its prey down. We know that it
could hunt animals as big as juvenile manners
because in a cave in Texas it’s been found
associated with its prey. That’s its distribution. And then there’s this
guy, miracinonyx. This is such a cool animal. This is a type specimen
from a site excavated in northern Nevada not far from
Pyramid Lake, Winnemucca Lake basin. This is the very skull
that led to the definition of this genus, miracinonyx. It’s called the
American cheetah, and it’s called the
American cheetah because this animal is so
similar in so many ways to African cheetahs
that for a long time it was thought that they
were really closely related. Some even thought
that maybe cheetahs evolved in the Americas,
crossed into Eurasia, and ended up in Africa. People who live
in the northwest, have been in eastern Washington,
eastern Oregon, Nevada, the Great Plains have probably
seen pronghorn antelope. Pronghorn are the
largest– pronghorn are the fastest herbivores
of North America. They can reach bursts of
speed of 60 miles an hour. There’s nothing
that can catch them. There’s nothing
that can come close. Why is this animal, it’s
reasonable to wonder, over engineered? Why are you able to run 60 miles
an hour when nothing like that is needed to get away
from your predators? Well, the guess
is– and a guess is all it is– that the pronghorn
is over engineered for today, but it wasn’t over
engineered for the past, that pronghorns evolved
with American cheetahs. And their speed is
accounted for by the fact that slow pronghorn became
dinner to the cheetah. Fast ones escaped. Here’s the distribution of
miracinonyx, American cheetah. It’s Western. The one thing I meant
to say and forgot is the fact that
fairly recently DNA has been extracted
from its bones, and we know that western
cheetahs aren’t closely related to African cheetahs at all. They are related to our cougars. They are similar to cheetahs
because their adaptations are similar, not because they
share a recent common ancestor. Ah, the giant rodents. They’re so cool. [LAUGHTER] Giant beavers were the
size of black bears. This is true. They’re the size of black bears. Different people
reconstruct their weights at different amounts,
but these were beavers the size of black bears. Mostly eastern in distribution. They don’t seem to
have been dam builders. Their teeth don’t match
the dam building habits of modern beavers. Mostly eastern in distribution,
but a couple of sites in the far northwest. And then these guys, capybaras. Capybaras today are the
world’s largest living rodents. Big males can reach 120 pounds. They still exist in
Central and South America. Here’s a family group of them. One of my students in
my extinctions class pointed out to me– I didn’t
know this a couple years ago– that they’re bred to be pets. If you Google capybara
plus pet, you’ll come up with totally
cool YouTube videos of capybaras living as
pets in people’s houses. If you do that, look
closely, and look at the wood in that house. There’s one YouTube– [LAUGHTER] Rodents have
ever-growing incisors. They need to keep
their teeth worn down. There’s a door in one of the
houses in one of the YouTube videos that’s totally–
almost totally– destroyed by chewing capybara, but
they are, to their credit, totally cute. [LAUGHTER] They hang around water
because that’s how they tend to escape predators. There were capybaras
in the– they are southern animals,
South American animals. Capybaras made it into
southern North America during the ice age, as did
another genus of capybara– this one, which was
at least 50% bigger than the modern capybara. This is a capybara also
found in South America that pushed 200 pounds. Here’s our second small animal. Our first small animal
was the short faced skunk. Aztlanolagus, the aztlan
rabbit, was about the size of a pygmy rabbit. Pygmy rabbits are fairly well
recognized in Washington State because there was an
isolated population in eastern Washington
that people are now working hard to reintroduce
in the Hanford area. Aztlanolagus gets was
a western rabbits. It was about the size
of a pygmy rabbit, but it didn’t behave
like pygmy rabbits. Its post cranial skeleton–
its legs suggested that its behavior was
more like a jack rabbit, that it was an efficient runner. There is its distribution. What doesn’t show on here are
records south of South America. This animal’ is known
deep into Mexico. Horses– many people
here probably know that horses evolved
in North America. They crossed into Eurasia
over the Bering land bridge. They also moved
into South America, where two different
kinds of horses existed until the
end of the ice age. They subsequently
became zebras in Africa. They continued to exist in
Eurasia into– obviously they still exist
into historic times, but they became extinct in
North America about 10,000 years ago only to be reintroduced
much later by Europeans. They were all over the place. Let me point out
that, whenever you see a picture like this
one, that’s showing an archaeological association. This is the archaeological
site of Wally’s Beach in southwestern Alberta which
has artifacts associated with an extinct horse. I’ll come back to that later on. Tapirs– tapirs
evolved in Eurasia and then moved into North
America and into South America. Don’t know how many
species there were. Maybe as few as two,
maybe as many as four, but they were found
from coast to coast. The flat-headed peccary. What’s on the screen
here is an animal that’s known as catagonus. It was discovered by
scientists in 1975. When scientists
discovered it, it was thought to be platygonus,
the flat-headed peccary, because it looks so much like. Its skeleton looks
so much like it. There’s no question
that platygonus, were we to see it on the hoof,
would’ve looked like this. This is the Chocoan peccary
from the Argentinian Choco. I should’ve said that. Flat-headed peccaries would’ve
looked very much like this. Platygonus was widespread
coast to coast. There’s that one record in the
far Northwest in the American Arctic. There’s now a second record–
it’s not been published– from the northern Yukon. It’s not been published,
so it’s not on here, but there’s no
reason to doubt it. So a widespread
peccary– we also know that this peccary
was a herd animal, and we know that
because, often when you find one skeleton of platygonus,
you find a bunch more with it. That’s very different from
the long-nosed peccary. The long-nosed peccary– when
you find one long-nosed peccary skeleton, that’s all you find. This pretty clearly
was a solitary animal. It was also an animal that you
find primarily in the wooded east. Camels– some of this
is hard to believe. I’ve been working with these
animals since graduate school, and I still find some
of this hard to believe. I’ll start with camelops. Here’s a reconstruction by
Wally Wolfenden of camelops. If you saw one today
walking down the street, you’d swear it was a dromedary. There are some differences. Its head is a little bit
longer, a little bit skinnier. Its hump is a little
bit further forward. It’s a little bit taller, but
it looks like a dromedary, and genetic– ancient
DNA– the analysis of ancient DNA from its
bones, which was just studied, shows that it’s more
closely related to Eurasian dromedaries than it is
to South American llamas. It was a western
camel– quite common. There have not been many
Pleistocene age, ice age sites in the Great Basin that
I’ve worked on that didn’t have camels in them. This is Wally’s Beach again. Wally’s Beach has
artifacts associated with both horse and camel. The other two extinct camels
are both lamas and lama size. Hemiauchenia was widespread. It was also a herd animal. We know that, again, because we
have found herds of them dead. Palaeolama not as widespread. Southeastern in distribution. Navohoceros– this was the
first reconstruction ever to have been done
of navahoceros. Wally Wolfenden and
I did this together. I did the anatomy. Wally did the hard part,
the part that takes talent. He drew this. When I saw this, I
thought it was remarkable, because this animal is exactly
how I would have pictured this. This animal is not
all that well known. It was between a deer
and an elk in size, but it had the bulk of an elk–
of a very large elk– and very simple antlers. It’s called a mountain deer
because its skeletons suggest that it was a really
nimble climber. Its skeleton has been compared
to the skeleton of a mountain sheep. There’s its distribution. Cervalces– this is often
called the stag moose. Found in two very different
places in North America. Major distribution obviously
in the east around the Great Lakes, and then a very
isolated distribution up here in the far northwest. These animals are
found in habitats that would be identical to
the habitats in which you find moose today. In fact, their post
cranial skeletons are– the skeleton
that’s not the skull– are very similar to
the skeletons of moose. So much so that they can
be very hard to tell apart, but the antlers are
distinctly different. Sooner or later– and
sooner is probably closer– the genetics of this animal
are going to be known. And my guess is it’s going to
show that these stag moose are closely related to stag moose,
cervalces, that occurred on over here in Eurasia, and that
these are genetically distinct. Nobody’s done that work. So here is a moose-like
animal that was not a moose. We’ve all– many of us
have seen pronghorn. I can’t say we’ve all
seen them, but many of us have seen pronghorn. Pronghorn existed
during the late ice age. One of the things that makes
pronghorn distinctive is this. What did I do? One of the things
that makes prong– I need three hands–
pronghorns distinctive is this prong on their horn. That’s why they’re
called pronghorn. Pronghorns have only two horns–
a left one and a right one. They existed in the late
ice age during the ice age, but they existed alongside three
other pronghorns, all of which have four, not two horns. Capromeryx was the
smallest of them. Capromeryx would’ve been
about that tall– 18 inches to two feet tall and
weighed about 25 pounds. The other two were
pronghorn in size. The difference between the other
two is that, in one of them, the horns were of equal height. In the other one, the horns
were of unequal height, with the front horns
shorter than the hind horns. Capromeryx–
reasonably well known. It’s an easy animal to
identify, because it is a tiny little pronghorn. Western North America–
tetrameryx not as well known, though you can see a
complete skull on the top right there with those
shorter front horns. Stockoceros is better known. There aren’t that
many sites of it, but some of the sites
that have provided the remains of
stockoceros have provided the remains of dozens and dozens
of them– 50 to 60 individuals. As a result, the skeleton
is really well known, and as a result, we know
that these were her animals. There’s no way the
capromeryx, the tiny one, the diminutive
pronghorn, could’ve been a herd animal
for the simple reason that it would have
been too inviting a target for a predator. Capromeryx was probably–
the diminutive pronghorn was probably an animal that
saved itself by stealth, and it probably had
protective coloring. Saiga– saiga are a
sad story in the sense of that saiga were doing
poorly for a long time in historic times. People launched a major, major
conservation biological effort to save them. It was working, and
then just recently they got really slammed by disease. It’s an awful story. They still exist in southern
Asia, but during the ice age their distribution went
from northern Spain and southern France– we
find them in the sites that I used to work on
in southern France– all away across into
northwestern North America. Euceratherium– the shrub ox. It also had the convenient
habit of pooping in dry caves in the
arid west, so we know a good deal about its diet. We know, for instance,
that it was a browser. It’s also western
and distribution, and we know from its genetics
that it was really closely related to the modern musk ox. Bootherium–
bootherium, for reasons I’ll talk about in a minute,
is called the helmeted musk ox. You can probably
maybe even see why up there– that heavy
mass of bone on its head. Widespread– you find in the
far northwest, the Arctic. You find it from coast to coast. It was found pretty
much every place in unglaciated North America,
except the far southwest and the far southeast. There’s why it’s called
the helmeted musk ox. For a long time, this
animal was divided into two different
kinds– the genus symbos and the genus bootherium. People began to realize
that, gee, when we find one, we often find the other. Maybe there’s something going
on here, and what’s going on is that one was the girl,
and one was the boy. [LAUGHTER] The girl has horns like the
modern musk ox has horns with a split down the middle. The boy has horns that look like
that– buttressed horns that are clearly meant to
be used in head butting battles for male male dominance. If you look at these horns, you
can see something else here, and I think this is really cool. See how these horns
curl outwards– this is the male– while
these are curving forwards? These horns are made
for head butting. These horns are not. The head butting was meant
to be just head butting. You weren’t meant to
hurt the other guy. You were meant to
intimidate the other guy. These horns curl
outwards so when these guys head butt neither of
them is getting stuck by horns. The female horns
point forward perhaps because that’s a more effective
way to ward off predators. I won’t talk– we’re
doing good for time. That’s the kind of thing
you’re supposed to say to yourself and not out loud. I won’t say much
about mixotoxodon. The toxodonts are
South American animals. We know from very
recent research that they’re most closely
related to horses and rhinos, but they are South American. Prior to the year
2013, we had no idea they got this far north. In 2013, Ernie [INAUDIBLE],
a very famous paleontologist, published the first record for
a toxodont in North America from eastern Texas. He told me about this two
years before it was published, and I thought Ernie, who
is quite old, had lost it. It just doesn’t seem possible,
but there is the tooth. This is a toxodont. Ernie will never lose it. He’s right. This is the only
specimen we have for this animal
in North America. The next one down is
in southern Mexico. Mammoth, mastodon–
everybody’s heard of mammoths. Many of you– maybe even all of
you– have heard of mastodons. I’d be surprised if many of
you who are not in the business have heard of gompotheres. Gompotheres were the
South American version of mammoth and mastodon. Mammoth and mastodon
did not make it south of Panama– the
Isthmus of Panama. South of there the proboscidean,
the elephant-like animal, was the gompothere. That’s what its jaw looked like. Gompotheres are
characterized by the fact that they have these
really complex cheek teeth. These are a lot like the
cheek teeth of mastodon, but they’re even more complex
than their cheek teeth. You can see how big they are. These were massive,
massive animals. Gompothere specimens have
been known for North America for quite some time,
but only recently– and I mean really recently–
was it realized how long they lasted in North America. We now know that from this
site called El Fin de Mundo that gompotheres
survived in North America until about 11,550 years ago. This is called a Clovis point. It’s associated with the two
gompotheres from this site. Here is the site. This site was excavated
by Lupita Sanchez– you see her name here–
and Vance Holiday. Vance Holiday was the
one who provided me with these illustrations. There it is right there. There they are excavating
that gompothere mandible that you just saw, and here are
what are called Clovis points. I’ll show you another
picture of these in a minute because I want to talk
about Clovis for a minute. Clovis is one of the most
famous archaeological phenomena in North America. It’s probably fair
to say that Clovis is one of the most famous
archaeological phenomena in the world. Clovis dates to between
11,600 and 10,800 years ago. It has an artifact that
is totally diagnostic. When you see it,
you know what it is. When you see it, you
know how old it is. When you’re an archaeologist
and you find one, you never forget where you
were when you found it. They are splendid artifacts. Like pronghorn, they seem
to be over engineered. People were importing
raw materials– gorgeous raw materials
all over the place to make these
beautiful specimens. Here is a cast of one that
I’ll come back to in a minute. Clovis sites are
primarily the sites of the planes and southwest. When people argue
that the animals we’ve been talking about were driven
to extinction by human hunters, it’s Clovis hunters
that they mean. One of the things that
characterizes Clovis is the fact that they made
what are called caches. Nobody knows why they did this. They’re amazing things. They dug holes in the ground,
left artifacts in them, and left them there. I’m mentioning this
one because there’s a famous Clovis cache in eastern
Washington near Wenatchee. It’s called the Richey Roberts
site or the East Wenatchee Clovis cache. There are about two dozen of
these known from North America. The Richey Roberts artifacts
are on the second floor in the Burke Museum–
not all of them, but enough of them to
make it worthwhile to go see them there. There’s also a
great ground sloth skeleton– megalonyx
skeleton– in the Burke Museum right near the Richey
Roberts artifacts found when they were
digging SETAC airport. That one has a
radiocarbon date, as I recall, of about 12,000
years ago– the museum one. Mastodon– mastodons are
quite different from mammoths. I will point to
that in a minute, but mammoths have
these high domed heads. Mastodons lack that. These are low, long tank-like
animals whose tusks jutted out kind of horizontally and whose
teeth were much more complex than the teeth of mammoth. Here’s their distribution. There are two archaeological
sites from North America that have both mastodon and
either Clovis age artifacts, or Clovis points themselves, or
Clovis dates– some combination of those two things. I put this up here just to
remind me of this amazing fact. There’s a mastodon known from
the Wasatch range of Utah at 9,800 feet elevation. People who are
interested in this stuff may notice that I’ve
only got two sites here that I’m willing to accept
as associated with Clovis age artifacts or Clovis age dates. What’s missing is this site,
the Manis mastodon site. It is a very famous site
in Washington State. It’s near Sequim, Washington. It’s now on a set aside. It’s being preserved. The little museum in
Sequim– you can go see the mounted skeleton
of the mastodon from there. Here’s the artifact–
wrong thing to say. Here’s the specimen that started
the big deal about mammoths. Many people think that this is
also a human associated site, and they think that because
of this particular bone. This is a head of a rib. Here are the articular
surfaces where the rib would have joined
with a vertebra, the backbone. And here is this
thing that appears to be sticking out of it. Many people think that this is
the tip of a bone projectile point. This, by the way, is– I
took this picture in– I shouldn’t tell you when, but
1977 when this was excavated. This is the way looked
right after it came out of the ground. This is the way it looks today
this is what paper published in Science in 2011. This is the location of that
rib and this thing sticking out. You can see the computerized
x-ray, the CAT scan there. It looks like a pointy thing. The argument is that
this is a bone projectile point sticking into a rib. I am unconvinced, and
here’s why I’m unconvinced, and I’ll just let you read this. This is a musth
battle, a musth battle between two male elephants. Not only do we know that
male elephants do this. We know that mastodons did it,
because there are mastodons known from the Great Lakes
area with skeletal damage that only could have been done as
part of this kind of battle. That skeletal damage includes
broken, shattered vertebrae. It is fully possible
that this piece of bone sticking into
the mammoth’s rib is part of that
animals own skeleton. Until it’s shown
otherwise, I’m not willing to accept this as
an archaeological object. Mammoth– we’re almost
done with our tour. Mammoths– the second iconic
mammal of the North American Pleistocene. People talk about two to
four species of mammoths. It’s now looking
from ancient DNA that all these guys could
probably interbreed. These were massive,
massive animals with massive, massive tusks. There is that dome
on its head that was meant to receive
the muscles that ran back towards
vertebrae, to an old up this massive, massive tusks. It looks very different
from a mastodon. 11 sites have been
found that have associations between Clovis
artifacts and mammoths. There’s no question that
people were hunting mammoth. I’ve been talking only about the
genus level here so far– genus level extinctions, and I’ve been
doing that because often it’s so hard to tell what are
properly defined species is with extinct animals. For horses, the genetics
suggest that there may be as few as two species. There may have been as few
as two species of horses during the late ice age. Paleontologists have
defined some of them 10 species, some
of them 20 species. So nobody disagrees
about the genus. A horse is a horse, but
there were three well defined species of animals that
went extinct in North America. The dire wolf is one of them. The genus canis still exists in
North America today– wolves, for instance, and coyotes, and
humankind’s best invention, the puppy dog. They all belong
to the same genus. Dire wolves were widespread. They had massive, massive
muscle attachments for the muscles that operate
their killing mechanism, their chewing mechanism. They were widespread. They were clearly social. There are 2,000 specimens of
saber tooth cats at Rancho la Brea. There are more than that of
dire wolves at Rancho la Brea. When one got stuck in the
tar pits, bunches of them got stuck at once, suggesting
they were hunting together. These were pretty
clearly pack hunters. They were pretty clearly
able to take down animals as big as bison. Panthera leo– this is
still hard to believe, but it’s still true. There were lions
in North America during the late ice age. Lions were extremely
widespread at one time. The Americas all the
way over into Africa– the difference about the
extinct American lion is that it was bigger than
the modern African lion. The genus still exists
in North America because jaguars are still found
in southern North America. And then there’s
the mountain goat. People here know
about mountain goats. They were introduced into
the Olympic Peninsula, where you can see them today. They were mammals of
the northern Cascades and northern Rocky Mountains. There was a very separate
species of mountain goat found in the southwestern
US– the Great Basin in the southwestern US– for
instance, in the Grand Canyon. We know that it had white
fur because that material has been found in dry caves
in the Grand Canyon. It was smaller than the
modern mountain goat, but it was also a
nimble, agile animal just as is the
modern mountain goat. Well, that’s my not
so quick rundown. I have 12 minutes left. That’s my not so quick
rundown of the players, the late ice age mammals
of North America . One thing that I have
been kind of avoiding so far, except to give you a
general notion as to when they became extinct,
is the chronology, the timing of their extinction. Remember, one of the arguments
for the loss of these guys is that the root cause are
Clovis hunters, that people entered North America. The first people
in North America were Clovis hunters–
and that they hunted these animals to death. That means that all
these animals must have existed during Clovis times. The problem is that
we can only show that 17 of these 37
genera of mammals made it past 12,000 years ago. We pretty much know
that they were all gone by 10,000 years
ago because there is not a single compelling date from
any site in North America that has these animals much below
10,000, but less than half of them can be shown to
have coexisted with Clovis. Some of these animals–
the most recent date predates 25,000 years ago. What we can be sure of is
that all of these animals were around 25,000
or so years ago. All of them are gone by
roughly 10,000 years ago, and a lot of them, but not
necessarily all of them, were going out of existence
between 12 and 10,000 years ago when Clovis people were around. The age old question is, why? The obvious answer
is climate change. I have published a
ton on this topic. People always associate me
with the climate change group, but the truth is
that nobody has made a coherent compelling
argument that climate can explain all of this, and I’m
just going to leave it at that. There is another explanation
that’s quite recent that you may have heard about. It made the popular media
just as kind of sexy science often does. That argument is that a comet
exploded above glacial ice in the Great Lakes
region of eastern Canada and caused these extinctions. That is, the extinctions are due
to an extraterrestrial impact. In fact, that
argument is not only that the extinctions were due
to an extraterrestrial impact, but that the end of
Clovis is to be explained by an extraterrestrial
impact, as are a wide range of other
things, including continent-wide burning
for which there is no evidence,
massive climate change, and a bunch of other things. All I want to do is
show you one slide. This is the chronology
of the latest dates for mammoth in the area where
Alaska and Eurasia come closest together. It’s called Beringia. Remember, that comet is said to
have exploded 10,900 years ago. If that’s the case,
their argument is that these extensions
all occurred around 10,900 years ago, but
as you can see here, our latest date for
Alaska is 11, 500. There are probably younger ones. Maybe they made it to
10,900, but our youngest date for a mammoth in
mainland northern Siberia is 8,700 years ago. Saint Paul Island–
5,700 years ago, and amazingly enough,
the youngest data Wrangel Island for a mammoth–
and these are really good dates. There’s over 100 dates
on mammoth from Wrangel– is 3,700 years ago. An impact event of
10,900 years ago which caused all these
extensions doesn’t work. And also remember that this is
one of the reasons I mentioned South America when I started. 37 genera became extinct
in North America. 54 genera became extinct
in South America, all the way down to the
tip of Tierra Del Fuego. It’s hard to imagine, even
without the slide I just showed you, an impact event
explaining all of that. Well, then there’s this. We may not have time
to get to my avocado. [LAUGHTER] There is a really intriguing
relationship between mammoths and avocados, gompotheres, and
ground sloths, and avocados, but I promised I
would only go an hour, and I only have about
eight minutes left. Human predation is clearly
the most common argument that you encounter
for these extensions, that Clovis people did
all of these animals in. The argument isn’t that Clovis
people hunted the carnivores to death. The argument is that Clovis
people hunted the herbivores to death and that because of
that their predators died, that saber tooth cats,
and scimitar cats, and American cheetahs
died because people did in their prey. I’m no fan of that
argument, and I’m no fan of that argument for
reasons that I’ve actually kind of already mentioned. Reason number one is this. We can’t even show that
half these animals made it into Clovis times. That’s reason number one. Reason number two is this. There are 37 genera of
mammals that became extinct, seven of which are carnivores,
30 of which are herbivores. Of those herbivores,
we can only show that people were associated
with them in such a way that they were
probably hunting them. We can only show that for
five of these animals. Here are the sites. We have one site with a camel
in it and a horse in it. We have one site with
a gompothere in it. We have two sites
with mastodon in it, and we have 11 sites with
mammoth, and that’s it. I’m sure I would be
gratified if you remember the distribution of ground
sloths in North America, but in case you’ve
forgotten, if you add them all up– all four of them–
they were all over the place. There’s not a single– not
a single archaeological association with ground
sloths in North America, even though they seem
to have been everywhere. There are other reasons I
don’t like these arguments, but these are the prime ones. We can’t show that people
were hunting these animals, yet they are said to have
hunted them to death. We can’t show that all these
animals, or even half of them, coexisted with
people, yet they’re said to have hunted
them to death. Well, unfortunately, the
conclusion to all this is that we simply don’t know
what caused the extinctions. The nice thing about
this– and this may sound odd– the nice
thing about this is the fact that we don’t know what caused
the extinctions drives people nuts, and because
it drives them nuts, it causes them to learn
more, and more, and more about these animals. Are you bored yet? [LAUGHTER] It’s 8 o’clock. SPEAKER 1: [INAUDIBLE]. DONALD GRAYSON: Avocado. [LAUGHTER] Avocado, OK. We’ve all seen
reconstructions like this. This is the 1972 reconstruction
from the National Geographic. It doesn’t matter that
it’s, what, 40 years old? There are the animals. We’ve talked about all of these,
and let me point something out. I just said that there’s
not a single association between artifacts
and ground sloths in North America that is
in any way convincing. Nobody even argues there is one. There wasn’t one in 1972,
but so deep is the assumption that people caused
these extinctions that, if you look here,
those are people hunting a Jefferson’s ground sloth. There is absolutely no
archaeological associations anywhere between
Jefferson’s ground sloths, megalonyx, and people. This drives me nuts. [LAUGHTER] But this is the view– I didn’t
show this to foam at the mouth. This is a common view. Here are some more of them. These are the reconstructions
that you see of the North American ice age landscape. It’s got the landscape
teeming with animals. Until relatively recently,
I kind of pictured the American past this way. I let myself think by analogy
with the African plains, the African Savannah that
North America was just covered with animals just
like it’s shown here. This, by the way, is from
the Great Basin, an area that we’re going to talk about
in a minute– high elevation Great Basin. And so let me quickly
talk about this. I think five minutes
is about right. Let me quickly talk about this. North America has four
botanically defined deserts. One of them is the Great
Basin Desert right here. Three of them are probably
better known– the Chihuahuan Desert, the Sonoran Desert. I think of these two
as Walt Disney deserts. This has saguaro cactus. This has Joshua trees. These are the three warm
deserts of North America. The cool deserts– warm
summers, cold winters. The warm deserts– hot
summers, warm winters. Here’s what the lower elevations
of the botanical Great Basin look like– kind like parts of
eastern Washington– sagebrush, and before livestock
were introduced, grasses. Here’s what the Chihuahuan
Desert looks like. I’m not going to talk
about it anymore. Loads and loads
of creosote bush. Here are Joshua trees
in the Mojave Desert– kind of an iconic plant
of the Mojave desert– and saguaro trees in
the Sonoran Desert. These are the warm deserts. The Great Basin botanical desert
has a diverse late ice age fauna. 20 genera of animals– all
of which we’ve talked about. Here are their pictures–
are known from there. It also has a really well
defined archaeological record. One of the two earliest
sites known from the Americas is from the Great Basin. It is from eastern Oregon–
called the Paisley Caves. It has human fossilized feces. I said turds before,
but I don’t want to say it again because
I shouldn’t have said it. [LAUGHTER] Dated to 12,400
years ago from which human DNA has been extracted–
Native American human DNA. This is one of the two oldest
sites known from the Americas. The other is a site called
Monte Verde in southern Chile that dates to 12,500 years ago. The earliest diagnostic obvious
artifacts from the Great Basin are also known from
the Paisley Caves. They’re known from
everywhere, but they’re best dated from
the Paisley Caves, and date to 11,100 years ago. These kinds of
artifacts are also associated with this cool
thing called a crescent. They’re widespread
in the desert west. We’ve got a really good
archaeological record from the Great Basin. We know that people were
here by 12,400 years ago and that they were
using points that looked like this–
artifacts that looked like this 11,100 years ago. We also have a good radiocarbon
record for the extinct mammals, and because of that, we know
that people were in the Great Basin at the same time as at
least these seven genera of now extinct ice age mammals. We know that people were
living in the same places where those animals live. That is, they
overlapped in dates and they overlapped in
habitat, and this made me wonder a couple of things. There is no association
between artifacts and an extinct mammal
whatsoever in the Great Basin. None. None that people
even argue about. There are no kill sites
from the Great Basin. That made me wonder about how
often people saw these animals. Were they as common
on the landscape as this reconstruction– this
common kind of reconstruction suggests? Or where they rare
on the landscape? Well, that made me
think about an article that I read a 19– I
read it before 1982. Richard Mack and
John Thompson were botanists at Washington State. I think Richard
Mack is still there. They sent me a manuscript
when I was a young puppy and said, what do
you think of this? And I read it, and made
some comments on it, and thought it was
cool, but I just didn’t get how
important it really was. What they pointed out was
that, unlike the Great Plains– let me put this differently. The Great Plains
has grasses that are adapted to being eaten by
larger herbivores like bison. The Great Basin doesn’t. This is what they pointed out–
that the Great Basin lacks widespread grasses
that do well when they are chewed by large herbivores–
when they’re grazed. That’s why when you
go to the Great Basin today in areas that
have cattle on them you see hardly any
grasses in the valleys. They concluded that large
grazers of the sort that we’ve been talking about here,
these large herbivores, were never abundant there. Well, it only took me
30 years to realize that maybe this is
worth thinking about, and what I started
thinking about was this– pointy, dangerous
things on tall plants, plants that my colleague
Connie [? Malark ?] calls ouchy plants. Connie is sitting right there. Anybody who’s a gardener,
when you prune your roses, you come away with stuff
that looks like this. Well, imagine being
a herbivore trying to eat one of these things. So I’m talking about plants
that have spines, thorns, anything that, if you try to
eat it, it’s going to hurt you. Their function is clear. They’re meant to provide
a mechanical defense against large herbivores. Well, guess what? The warm deserts–
Mojave, and I’m not going to worry about the Chihuahuan. The warm deserts of
western North America– the Mojave and
Sonoran Deserts– have over 100 species of these ouchy
plants, these mechanically defended plants spread across
21 different plant families. They look like this–
catcclaw acacia– there’s its
distribution– or this, or this, or this with these
very pointy, spiky leaves. These are plants that
have that armament to keep large mammals
from eating them. How about the Great Basin? There’s only six species in
six families of these things in the Great Basin. Here are three of them
with their distributions. That’s a huge difference. Over 100 species in
the warm deserts, only six species in the
Great Basin cool desert? Somehow you cross a boundary
when you go from here to there, from mechanically–
from tall plants that are mechanically– pardon me. From the lack of
tall plants that are mechanically armed
to an abundance of them. And by tall plants,
by the way, I mean plants that are
over six feet tall. Lots of them down here. Hardly any of them up there. I am calling that the mechanical
defense line, because that’s what this represents–
a line that bounds a place where plants
are defending themselves with mechanical devices. Obvious question to ask
is, what created this line? Obvious answer is that it
was created by climate. After all, we’re going
from a cool desert to a warm desert or vice
versa, and sure enough, when you look at the
history of these plants, that does explain some of it. For instance, yellow
paloverde, parkinsonia, doesn’t reach its northern
edge of its distribution until about 4,000 years ago. It had to wait till it warmed
up until it could get that far north, but that doesn’t
account for all of this. Catclaw acacia with those really
scary things– catclaw acacia was in the Grand Canyon 22,000
years ago during the late ice age. Joshua tree was at the northern
edge of its distribution by at least 18,500 years ago. Climate can’t account
for all of this. What I think does account for it
is the distribution of huge ice age herbivores, the
animals these plants were defending
themselves against. Here are the heights of a
subset of those 100 species. There’s no herbivore today
that can reach up 50 feet and eat the top of
an acacia plant. Doesn’t happen. Here are the heights of
the biggest herbivores in arid western
North America today, and just to be as
fair as I could, I include bison on there even
though bison are looking down to eat and not up. These animals are
not tall enough to account for these tall
mechanically defended plants. The animals that can account
for this are all now extinct. So my guess is that, as we
move north from down here up into this area, the
botanical Great Basin, we move from an area where
these animals were relatively common to an area where they
may well have been quite rare. That perfectly
matches the argument that Mack and
Thompson made in 1982. Well, when I first
made this argument, I don’t remember if I was
talking to this person or sent him a manuscript
that talked about this. None of this is
published, by the way. He asked me– this is Dave
Rhodey, a paleobotanist, one of my own students who’s
often done this to me. He said, don’t extinct
herbivores ever look down? By which he meant, why are you
only looking at tall plants? Why don’t you look at
the short ones, also? That annoyed me, number one,
because I hadn’t thought of it, because certainly extinct
herbivores would look down, and number two because
it meant a lot more work, and I thought I was done. [LAUGHTER] So now rather than looking
just at the tall mechanically defended plants, I looked at
the short mechanically defended plants, and guess what? There is no difference in the
distribution of these plants. Short plants are
mechanically armed as often in the cool Great
Basin Desert as they are in the warm
southwestern deserts, leading me to wonder why climate
would matter to a plant that was seven feet tall, but not to
a plant that’s five feet tall. The only thing that
can explain this is the height of the
herbivores and the abundance of the herbivores that
existed in this area in the late ice age. So this is the argument, and
I promise I’m almost done. I’ve gone one hour
and two minutes, but we’ve reached this. [LAUGHTER] I’ve noticed that I walk down
the ave holding an avocado, people applaud. Now maybe I understand why. There’s an avocado. Avocados are amazing. These obviously are kind
of domesticated avocados, but the difference between
wild avocados and this guy is the pulp of the fruit. It’s not in the seed. The seeds of a wild
ones are this big. This is obviously
an avocado seed. You see a fruit like
this or a seed like this, the obvious question to ask, if
you’re smart enough to ask it– and I wasn’t. It was Paul Martin and Dan
[? Jensen ?] in the 1980s who asked it and answered
it– is here’s a big fruit with a huge seed. Why? What could have possibly eaten
this and distributed the seeds across the landscape? Well, it’s things
like gompotheres, ground sloth, mammoths. They’re all gone today. It’s called a megafaunal fruit. Megafaunal fruits
are large fruits. Here’s lots of
characteristics of them– large fruits with large seeds. The seeds could pass through
the guts of an animal and still be able to germinate. In fact, some of the
seeds of megafaunal fruits have to pass through
the guts of an animal to be able to germinate. That’s the avocado story. When you buy avocados
when you eat guacamole, think to yourself that
this plant clearly evolved in the presence of
gompotheres, ground sloths, and other large things that
were eating it and distributing its seeds. Well, there’s at least
10 different species of plants with megafaunal
fruits in the warm deserts of the southwest. There is not a single
one in the Great Basin. That matches the distribution
of mechanically defended plants and Mack and Thompson’s grasses. Sloth poop. Shasta ground sloth, sloth poop. Many people think–
and that includes me– that the dispersal mechanism
for the large fruits of Joshua trees– these fruits are
characterized by the fact that not only are they
large, but they don’t break open on their own. They’re called indehiscent. They don’t break open
and spread their seeds. Many people think that
one of the prime seed spreaders of yucca
trees– of Joshua trees. Excuse me– of Joshua trees
during the late ice age was the shasta ground sloth. It would eat those fruits. It would wander
across the landscape. It would drop this
someplace else. Then Joshua trees would emerge. That, they argue, is why we have
a distribution of Joshua trees that looks like it’s declining. That is, that the primary
disperser of this planet is now gone, and as a result,
the plant is in retreat. And sure enough, the late
Pleistocene distribution of Joshua trees looks like this. So that means to me as we
go north in the arid west we go through an area
where large mammals may not have been common, but
they were common enough to lead to those diverse set
of mechanically armed plants and to plants with
megafaunal fruits to an area where animals–
large mammals may have been quite rare. Well, the other
question to ask is this, and I’m not going to
answer because I’m done, but the other question
to ask is this. Did any place in America
actually look like this? There was recently a
reconstruction of biomass, the number of animals on
the landscape in Alaska, that determined that
Alaska didn’t– not only– how do I put this? That a version of Alaska
that looks like this vastly underestimated what
Alaska looked like. In fact, we don’t know that
for any part of North America. The next question
to ask in this vein is just that– is there any
place in North America that looked like this? And as part of that,
the other question that’s going to continue to
be asked is, what in the world caused the extinction
of all these things? And with that and an hour and
five minutes after I started, thank you. [APPLAUSE] Thank you.

Reader Comments

This is one of most comprehensible videos on Ice Age megafauna in North America. Regarding the reason for the extinctions I would ask Professor Grayson to read my book 'Ice Age Extinctions, A New Theory' which was recently published.

I don't like his interpretation of lots of dire wolves in Le Brea. They very well may have hunted in packs like modern wolves. But I have to argue that the smell of other dead animals in the pits would attract predators and concentrate a bunch into the pits. They could be coming one at a time. When I see a dead dear out in the country its usually surrounded by at least 3 coyotes but coyotes are known to mostly hunt solo.

Human beings were a key reason why these Ice Age megafauna became extinct, after all these animals survived prior glacial and interglacial cycles. It is no coincidence they went extinct when we came unto the scene.

As for 'cause of extinctions,' the climatological 'excuse' is pretty much dead, particularly when you examine the dating of megafauna extinctions around the world. End of Pleistocene extinctions start in Africa about 20-25 thousand years ago, then through Europe, across Asia, and then rapidly through North and South America. It is LIKEWISE 'noticeable' that populations of mega-fauna isolated on islands were NOT afffected in any way by climatological changes, persisting for thousands of years after all mainland populations became extinct, which could simply not be the case if 'climate' were the primary, or even a secondary cause.

I'm of the opinion that the Earth gets impacted by a large object from space at frequent intervals. Most hit the oceans. Extinctions that happen over relatively long time periods can be explained by multiple impacts. Oceanic impacts can cause huge tsunamis, super hurricanes, and climate changes. Ocean impacts are not payed enough attention to when looking at extinctions and past climate change. It is something I find is a glaring mistake and is ignored by the scientists who should know better. The truth will come out, eventually. Maybe even the Biblical Flood will be explained as well. Come on guys, it isn't rocket science.

In my opinion, climate change was the main problem for ice age adapted animals like cave lion mammoths and smilodons. And human interference only accelerated the death rate. I believe if humans did not evolve. Than animals that went extinct atthe end of the ice age, just would have evolved to be more suited for the increasingly warmer weather. But since human hunting accelerated the death rate, animals just didn't have time to evolve.

Also, I have a theory that if human did no exist, elephants and lions would have become the dominant animals due to them spreading across the world and into the Americas, and everywhere they went, they completely took over the ecosystem

I think I need to tell you what froze out the mamamouth.It was a ice coment that came to close to earth with a long ice tail it's like cabin pressure at 30thousand feet up at 600 miles per hour. You freeze solid in about 12 to 23 seconds.when there is no cabin pressure you freeze solid in seconds.

Ice coment started the ice age froze out every thing for thousands of years it could hit some where again 364.4 degrees below zero with wind chill factor to boot.For thousands of miles wide I know it would freeze me to death I'm cold at 10 degrees wrapped up good to wrapped up any more I can't walk.when you find out how to crawl down in a tank of liquid nitrogen.without freezing let me know

The hunting theory is so pathetically weak it defies logic. When Europeans came to No.America it was teeming with wildlife and native humans were everywhere. The animals at that time were much smaller than the extinct ones. By the hunting theory logic, all animals should have been extinct given the relatively dense human population (compared to 10,000 BC). Plus the size of the extinct predators is really terrifying and puny humans would have been prey. Also after a kill the predators will show up and guess who's likely to win?? The hunting theory is DOA on the start line.

The more interesting question is why these extinct megafauna genera survived the six interglacial periods of the last 2.5 million years but not this current one. OR were there similar megafaunal extinctions during those interglacials we don't know about?

I live in the Sonoran desert and paleobotanists say the flora was much different >15,000 BP when most of the megafauna disappeared.

Excellent presentation. Grayson provides the best arguments i have seen why hunter-gatherers could not have caused the magafauna extinction. Most of all, i love it when a researcher can simply say how we just don't know yet.

Excellent presentation. Grayson provides the best arguments i have seen why hunter-gatherers could not have caused the magafauna extinction. Most of all, i love it when a researcher can simply say how we just don't know yet.

How does an extinct mammal never appear in North America again, unless re-introduced later on?..how can something that is extinct (doesn't exist anymore) get re-introduced at a later time??????? Serious question, and I want a serious answer!!!!

Um bone point he talked about has been reported to be bison bone. If correct I do think that creates a problem for his hypothesis. I am also aware of mass kill sites of Long horned bison. No question about it. Time Team America did a show about it. Osage orange and one kind of locust have nasty thorns. There is also a location in CA where the sides of a very large stone has been rubbed smooth at a height that limits the options to Imperial Mammoth.

this bloke reeks of confirmation biases and doesn't have the capacity to truly contemplate a different perspective than the one he learnt 50 years ago!?No wonder we can't progress as a species with this level of closed circuit thinking..😕

I'm confused – in about the 27th minute he's saying horses went extinct in North America until they were re-introduced by Europeans. If that's right then my mental image of early western explorers encountering native Indians on horseback can't be right can it? I'm perfectly sure my mental image is far from accurate, but surely the bit about them riding horses was right, wasn't it?!

He is in Washington and not one mention of the black mat or the scablands flood? It is in his backyard. 50 foot high, 5 mile wide current ripples on the ground, dry falls and so on is not worth one slide in the presentation? I am not expert but "no evidence of mass fires"? What is the black mat layer? Great info on the animals themselves, but lacking in the event that killed them. Are universities echo chambers? I don't get how evidence is just dismissed. I would rather hear why he thinks this is not a factor rather than just not addressing it.

There actually is evidence of humans consuming ground sloths: http://www.cbc.ca/news/technology/mega-sloth-likely-on-humans-ice-age-menu-1.1143512

The fact that humans drove the late Pleistocene extinctions is, frankly, indisputable. There is no better explanation for the simultaneity of extinctions on three continents and several large islands, and even possibly Europe, Africa, and Asia, with the arrival of humans to these regions.

Climate change theorists simply do not have much of an argument; these animals had survived worse shifts in climate, so why did this one kill them, and why so sporadically?

The hypothesis is not necessarily that humans hunted them all, but that they impacted their environment enough to drive megafaunal extinctions, via a variety of mechanisms, possibly including overkill, burning land, clearing forests, introducing diseases, and even just competing with native fauna.

I enjoyed this presentation but I also have a bone to pick with it. To question the extinction of megafauna in South America due to a North American impact is to ignore the demise of the Dinosaurs, world wide, due to a Central American impact. This is the same thing as calling a time in the past that had co2 levels of 2,000 ppm a climate optimum and then calling our current levels of a paltry 450 ppm global warming. If the co2 levels were to drop to 175/150 ppm all life would end on earth. We don't have science, we have dogma. Dogma is a cancer. Also this guy is completely ignoring sites in Virginia that show human Solutean (European) habitation 14,500 years ago. Prior to Clovis. As I said…Dogma is a cancer.

The answer to what caused the extinction is right there in his slides. There were none of those animals anywhere near the Hudson Bay Area. That’s because there was a polar shift. The North Pole was once centered in that area. That’s what created an ice free corridor and eventually a bridge from Asia to Alaska. That’s why you see some of those animals reaching up into Alaska but not further Northeast. The climate shifts and zone changes killed off many animals. This was felt way into Siberia where mammoths in plush Savannah were suddenly plunged into the cold. That’s why we find so many preserved in pristine condition in the permafrost. They were almost flash frozen by the polar shift to its current location.

47:00 my first thought looking at the "spear tip" stuck in the ribs, was how could they possibly generate enough force even on level ground to stick that in there?. I am aware of spear slings but still probably a mating thing

Here is a thought all these animals we will take the horse for example you keep saying this species of horse is extinct. Well maybe its not a separate species of horse but just a different ethnicity but still just a horse. I mean humans have different ethnicity but we don't say an Asian is a different species of human. Those are all horses just a different ethnicity just like humans have. And just because a species has a bigger version of itself in a different area does not make it a separate species either. Deer in the south are much smaller than deer in the North but they are still white tail deer. I'm bored with scientists acting the way they do trying to claim their own discovery of a new species of animal. No dude you just found a different looking moose but its still just a moose.

He laughs at Impact Hypothesis cause he stupid as fuck, and think its only one thing that is cause the extinctions, why not all, comet or asteroid hits, caused all of the problems, life strugles, and humans that survives catastrophe hunts what they could and whats left, to fucking survive, and plus climate change that occurs because of impact, all geology records and proxies shows that fucking impact happend, for fuck sake there is over 500.000 oval shaped craters all over North Carolina, all oriented in one direction, so fuck you mainstream academia you stupid ignorant egoistic fucks, grow fucking up, open your mind a little bit, do not be so shallow and limited like cans

What I don't understand is that, if the extinction of mammoths and saber tooth cats, among other fauna, was caused by overhunting by a handful of primitive humans with spears and stone axes, then why, after guns were invented hundreds of years ago, weren't elephants, lions, tigers and bears completely wiped out as well? They still exist, even though humans had multiplied a million fold and created weapons of mass destruction. I don't think this theory holds a drop of water.

There is so much wrong with this presentation, but I first want to thank the presenter for clearly and pleasantly sharing his thoughts (whatever their merits) and thereby allowing a serious discussion of this important topic. First, let me say that he omits very important extinctions and glosses over surprising survivors. But it is his general theses, namely, that (a) humans could not have been responsible for the collapse of the American megafauna, and (b) there cannot have been Africa-like herds of megafauna in Pleistocene North America, which must be refuted. The learned professor suffers from myopia in his attempts to view the ancient world. Humans, especially hunter-gatherer groups, are incredibly sophisticated hunters.

The evidence of their hunting might not be great after thousands of years for a variety of reasons, including hunting methods that don't lend themselves to preservation (such as all-wood arrow shafts and tips as in New Guinea), cultural practice relating to butchering and disposal of game (do they just cut out the meat they can carry when game is plentiful or do they remove meat and bones?), and simply chance (how many evidences of hunting are preserved and how many of those are likely to be found by and correctly identified by paleontologists?).

What few people realize is the simplicity that lies behind any mass extinction that doesn't affect all members of a faunal community (e.g. we lost mammoths, mastodons, gomphotheres, ground sloths, camels, horses, and tapirs in what is now the USA, but camels and tapirs survived in South America, and elephants (mammoths were just elephants) survived in much of Asia and most of Africa; also, Eurasia lost its muskoxen, but North America retained them). And here it is: more animals died than were born for long enough to ensure no more could be born.

This sounds too obvious, right? But it's not, and greater minds have failed to grasp it. The animals which went extinct did not do so all at once. Yes, most seem to disappear by X date in North America or slightly later in South America, but, as pointed out in the presentation, there were seemingly random holdouts in other areas. All it would take for humans to be the proximal cause of the extinction of a species is for whatever pressures humans place on that species to be just enough more to cause a negative birthrate. When that happens and is sustained for centuries, animals which birth fewer young and whose young take longer to raise are doomed, but so are animals which might have an average amount of young for a larger animal but which live in already strained conditions (low densities due to competition with other animals, fragile environments, etc.). Think of the old saying about the straw that broke the camel's back. It comes from the reality that there will always be a tipping point: a camel's back can only sustain X amount of weight, and, in truth, it would be possible to cause a failure by placing that maximum amount of weight on the camel and then adding a single straw.

If you look at extinctions around the world, you find that they do not correlate with unusual or even sever climate change. Muskoxen survived the end of the ice age just fine in the North American Arctic and in Siberia only to become extinct in Siberia thousands of years before the present. Elephants survived in China, Southeast Asia, South Asia, and parts of the Near East (in addition to virtually all of Africa) until the rise of Rome (more or less), but they were lost in Europe, the Americas, and northern Asia. However, if you focus on post-Pleistocene extinctions and extirpations, you can find a pattern: the elephants of Eurasia, which survived the transition to the Holocene, begin to disappear from the Chinese heartland the the Near East before the time of Christ. Some centuries later, the elephants of North Africa are gone. By the time of European colonialism, wild Asian elephants do no exist west of India or north of Nepal and South China and they are gone from populous Java. By the dawn of the 21st century, wild Asian elephants are virtually extinct in China, Vietnam, Cambodia, Laos, and are so fragmented in much of Indonesia, Burma, and India as to be nothing more than isolated genetic islands of wild elephants. In Africa, they are similarly fragmented; the bush elephant is almost completely confined to heavily managed game parks, and the forest elephant, though less managed, is vanishingly rare. Rhinos have fared worse. 3,000 years ago, they were found from the extreme west of the Indian subcontinent all the way to the Yangtze in China, and from the Yangtze all the way to Java. By 1,000 years ago, the three species of Asian rhino were gone from China and were contracting to the north and east within India. By 10 years ago, the Indian one-horned rhino numbers in the low thousands, the majority of which occupy a single park in India's extreme northwest; the lesser one-horned rhino (renamed the Javan rhino for the following reasons) had lost its last continental population of rhinos in the 2000s and was reduced to fewer than 100 individuals in the far west of Java; the Sumatran rhino, which, again, was actually once found from China to Indonesia, was similarly reduced to a tiny number of individuals, most in Sumatra, with little hope of surviving the century.

As sad as it is to say, for all of our wonderful extant megafauna (three elephants and the rhinos of Africa and Asia), they have not birthed more offspring than the adults they've lost for at least the last 3,000 years. In other words, they are going extinct. They are functionally already extinct. We who are having this discussion just happen to be witnesses to the later stages of an extinction event that began thousands of years ago. If it can take 4,000 years to kill off the biggest game animals on the biggest land masses, how long would it take to do so on land masses which are much smaller? The answer, obviously, is less time would be needed. If, then, humans were the straw breaking the camels back in the Pleistocene, what difference might there be for game that had never been hunted by hominids versus game that knew humans as predators? Again, if you look at the distribution of extinction sin the Old World, you'll see that the areas where modern humans went first (Africa, the Near East, South and Southeast Asia) show fewer extinctions than areas where primates were newer members of the fauna (Europe, Siberia). When they crossed into North America, not a single game animal would have recognized them as predators. Hunting would have been dangerous only because of the other dangerous predators, which, no doubt, these first humans would have hunted aggressively for both defensive reasons and, likely, religious reasons. If they entered 15,000 years ago (a rounded number, but I think it's likely they arrived earlier than is generally accepted), all they would have to do is cause enough extra deaths each year for a a few thousand years, and all the megafauna would go extinct. Importantly, they needn't hunt any one animal much in order to accomplish this. If mammoths could only sustain a 10% mortality rate, and humans made it a 15% mortality rate, the mammoths would go extinct in a matter of centuries, but the vast majority of all mammoths right up to the end would die of natural causes.

Because the above IS why the megafauna went extinct (and continue to do so), it will never be possible to prove. But we can infer this truth by looking at when megafauna have become extinction, which megafauna became extinct, and where they became extinct. Here's a summary:

Mammoths and rhinos are extinct in Europe by the end of the Pleistocene.In North America, only three land herbivores of 750 lbs or more survive (elk, moose, bison); all others are extinct by the end of the Pleistocene EXCEPT the ground sloths of the Caribbean, which live on for thousands of years into the Holocene.In South America, no herbivores of more than 750 lbs survive to the present; all are dead by 10,000 years ago (with the possible exception of one gomphothere, about which claims are made for a late survival)In Asia, the last mammoths survive until 8-9,000 years ago on the mainland, but on one arctic island they survive till the rise of modern civilzation.In Africa, most big game survives into the Holocene, but on Madagascar, all giant lemurs, giant flightless birds, and hippo species are killed off between 1,000 AD and 1700 AD.In Australasia, all giant marsupials, giant land turtles, and some giant flightless birds become extinct 40,000 years ago (some 30,000 years before any other continent loses its megafauna), however, this only applies to the mainland: on offshore islands, such as New Caledonia, giant land turtles survive until a few thousand years ago.In New Zealand, the giant flightless birds and giant eagle (among other species) survive until about 1200-1300 AD.In the Galapogos Islands, where humans never lived, giant tortoises and giant lizards continue until the islands' discovery by Europeans.

No one event can correlate to the loss of all animals over 200 pounds in Australia 40,000 years ago, the death of all but three herbivores larger than 750 pounds in the Americas 10,000 years ago, and the similar loss in Europe about the same time. Nor can it correlate with the retention of megafauna in Madagascar, NZ, Cuba, etc. until well into the Holocene. But if you correlate these extinction events with the coming of man, you begin to see a patter. Modern man hits Europe about 40,000 years ago (if not earlier), and the megafauna are gone within a few ten thousand years. He reaches the Americans 12-20,000 years ago, and the megafauna disappear within a few thousand years. He reaches the Caribbean about 5+ thousands years ago, and then the last ground sloths, whose Florida cousins 70 miles away had been extinct for 6k years, disappeared–same for NZ and Madagascar 800 y.a. We did it!

The distribution suggests that the lack of distribution over the northern part of North America is because the ice sheet scrubbed the land clean. The animals would have followed the edge of the ice as the ice sheet melted but met man at the end of the most recent glacial period. As for the argument that man was responsible for the demise of these animals, the survived cycle after cycle of glacial-interglacial periods. The only difference in our present Holocene interglacial is that man had arrived.

No proof of massive fires associated with the ET impact hypothesis?? I believe there is plenty of excavated proof. The Mammoths at 3700 and 8700 BP were NORTH and WEST of the majority of ice sheet source of melt water that would have caused the floods that contributed to the extinctions. Why not mention the younger dryas ice age and how suddenly it happened? Why not mention the scab lands and dry falls and the possibility that they were formed in one massive flood from the ET impact on the massive glaciers in canada?

I've never understood how any paleontologist or archaeologist could seriously propose the theory that a bunch of paleolithic hunter-gatherers in widely scattered (and tiny) communities could have hunted hundreds of species with tens of thousands of members each to extinction. It's absurd on its face. Even a cursory glance at the thousands of mammoth (and many other species) smashed, torn, crushed and buried in the frozen muck of Alaska and northern Canada tells a very different story. Something catastrophic ended the last Ice Age, and the mega-fauna with it.

Think of the tameness of animals of antarctica! If animals like the giant sloth could be killed by walking up to them and pounding them on the head with a rock, what reason would there be to use a valuable piece of flint? If you could walk up to a horse and cut it's throat, how would you lose a spear point?

I cant seem to find a job but for some reason i found the oldest looking and biggest spear points in north america in virginia. This is true. The next story is made up but could happen. I was 18 years old and a freshman in college. The class was working on a project for National Geographic. We were working a pre clovis ice age site in virginia. Being the strongest in the class i was giveing the job by the female teacher driveing the wheelbarrow. It was hot that one day so i took off my shirt off and i think the teacher noticed how big my biceps were. it was getting towards the end of the day and she came up to me and said '' can you stay after class an extra hour i want to show you how to dig around the mammoth bone without breaking it. so i said ok. She was very clovis looking. Brunette long legs, busty, about 40 years old. The soccer mom type. I was watching her work on her hands and knees. I cant tell you the rest of the story its x rated. Until next time.

Simple logic kills the hunter extinction theory very quickly. All you have to do is consider the millions of natives in North America prior to Europeans, say 1500 CE to be generous. The natives had thousands of years to perfect their hunting skills and refine their equipment to kill animals. The wild game was much smaller than the extinct megafauna. But yet this large population of natives obviously could not kill a small mammal (and tasty) to extinction, yet its relatively easy to hunt and kill compared to a giant bison or mammoth. Plus you are not likely to be injured while taking down a deer vs a mammoth.

Species in North America did not go extinct(or nearly) until the introduction of cartridge ammuniton and larger accurate firearms, i.e. bison and carrier pigeon). Even with several hundred years of muzzle-loading firearms the wild game was nowhere close to being wiped out. And we are supposed to believe a relatively small number of primitive people armed with 6 inch stone spearpoints killed off all these giant beasts?? Ludicrous theory at best!

Its a good example why "scientists" are viewed with skepticism because some of them don't use common sense with their pet theories. I do strongly agree with Professor Grayson's thoughts on the extinction theories. Catastrophic events like volcanoes kill off large numbers of animals over large areas. A good example is the Ashfall area in Nebraska. You have a quick kill off of many animals and the survivors starve to death and/or get overcome with disease with weakened immune systems. A couple large volcanic events and you've got world changing die offs of animals and plants.

I still think it was in large part due to the comet strike on the glacier. This created the Carolina bays. Only seen clearly with lidar. About the diminutive size of herd animals making them not herding in behavior. I went to England in 1996, and Muntjaks had been introduced. Very small Southeast Asian deer. Obviously herding and very tiny. Picture a cat being chased by a large dog. The cat runs under a car and is safe. Safety in numbers is the answer, because the tiny deer have lots of eyes looking for trouble. The comet effected the breeding genetic diversity, and took a while to come forth after the genetic bottleneck caused by the comet.

We are still in an ice age. That's why the poles are filled with ice. What we are in right now is an interglacial period (or "glacial minimum"). The eras that people think of as "ice ages" are called "glacial maximums". In the 4.56 billion year history of the earth, the polar regions have been ice-free more than they have been ice-bound.